The invention relates to the detection and evaluation of the strength of leaks situated on the head of a nuclear reactor vessel filled with pressurised water at high temperature.
The leaks are detected and evaluated using a tracer gas: the water vapour itself, which comes from the leak under investigation.
One particularly important application of the invention consists in the detection of leaks in penetrations of pressurised water nuclear reactor vessel heads. The penetrations in question are those which allow the control rods of the control rod clusters to pass through. Early detection of such leaks allows the operator to bring the installation to a safe fall-back operating condition.
Techniques for detecting leaks in vessel head penetrations are already known, derived from those used for detecting leaks in heat exchangers. Many solutions use monitoring by dilution of a :radioactive tracer. In certain devices, this solution, using monitoring of the particle radioactivity, leads to detection thresholds and integration times which are high because of the extreme dilution of the tracer. Other known solutions do not make it possible to give any direct indication as to the strength of the leak, and have the drawback of being essentially qualitative.